1. Field of the Invention
The present invention pertains to low-polydispersity copolymers useful for photoimaging and photoresist compositions, and to the photoimaging processes which use these compositions. The low-polydispersity copolymers of this invention are prepared using controlled radical polymerization (CRP) techniques such as RAFT (reversible addition fragmentation chain transfer) polymerization.
2. Description of Related Art
Polymer products are used as components of imaging and photosensitive systems and particularly in photoimaging systems. In such systems, ultraviolet (UV) light or other electromagnetic radiation impinges on a material containing a photoactive component to induce a physical or chemical change in that material. A useful or latent image is thereby produced which can be processed into a useful image for semiconductor device fabrication.
For imaging features at the submicron level in semiconductor devices, electromagnetic radiation in the far or extreme ultraviolet (UV) is needed. Photolithography at 248 nm exposure is currently in commercial use, and 193 nm exposure is currently being introduced for microelectronics fabrication using design rules for 0.13 μm and below. Photolithography using 157 nm exposure may be needed for 0.07 μm or lower design rules.
Photoresists comprising copolymers with fluoroalcohol functional groups have been disclosed in WO 00/67072.
Copolymers of fluorinated alcohol monomers with other comonomers have been reported (U.S. Pat. No. 3,444,148 and JP 62186907 A2). These patents are directed to membrane or other non-photosensitive films or fibers, and do not teach the use of fluorinated alcohol comonomers in photosensitive layers (e.g., resists).
There is also increasing interest in developing polymerization processes that can be predictably controlled to produce polymers having a specifically desired architecture and molecular weight. One of the means for achieving such results is through a process of “living polymerization.” Such a process provides a higher degree of control during the synthesis of polymers having predictably well-defined architecture and molecular weight with narrow dispersity as compared to polymers made by conventional polymerization processes.
RAFT (reversible addition fragmentation chain transfer) polymerization processes have been disclosed for the preparation of low-polydispersity polymers from acrylic, styrenic and selected other vinyl monomers. (WO 98/01478, WO 99/31144 and EP 0 910,587). Fields of application for these RAFT-derived polymers include imaging and electronics (e.g., photoresists).
T.-Y Lee et al., (Advances in Resist Technology and Processing XX, Theodore H. Fedynyshyn, Editor, Proceedings of SPIE, Vol. 5039 (2003), pp 548-557) have disclosed the preparation of acrylate terpolymers using RAFT processes. They also disclose the use of controlled radical polymerization (CRP) processes for the copolymerization of fluorinated norbornenes with norbornene, and the copolymerization of norbornenes with acrylates to be used in 157 nm photoresists. Yields of the polymers are low, and molecular weights are very low (Mn<3700) in all but one example.
There remains a need for photoresists with high transparency at 157-248 nm and good resolution to enable the production of electronic components with smaller and smaller feature sizes.